1. Field of the Invention
This invention relates to a method of distilling crude fatty acids, and more particularly to a method of degassing, dehydrating and preliminarily purifying the crude fatty acids prior to being distilled, as well as to an apparatus for accomplishing such a method.
2. The Prior Art
It has been known for a long time that, in the straight-run distillation of fatty acids, the quality of the fatty acids obtained from the main distillation stage can be improved, i.e., the amount of undesirable components therein such as carbohydroxides, aldehydes, ketones and peroxides reduced, if these precut (lower boiling) components are separated out of the crude fatty acid in a preliminary step prior to reaching the main distillation stage. Such separations have been conducted in the past at the same time as the conventional dehydrating and degassing steps which have almost always been accomplished under the same or nearly the same pressure conditions as are found in the main distillation stage, i.e., at 2.66 and 40 mbar. However, these known processing procedures have the disadvantage that the lower boiling (precut) components are only partially separated from the crude fatty acids.
The lower boiling components result from oxidative and/or thermal conditions to which the crude fatty acids are subjected prior to and during the distillation thereof, such as during oil and fat removal steps, cleaning, storage and separation steps. During these procedures, the oxidative and thermally sensitive acid components, which are more or less unsaturated, are exposed to high thermal and/or oxidative conditions even when the treatment apparatus is well sealed, and small amounts of cleavage products result. This is especially true with crude fatty acids which are very unsaturated, i.e., they have more than one double bond in the molecule, and specifically when the acids are subjected to high temperatures in the distillation apparatus. These cleavage products undesirably appear in the main condensate in prior art processing systems.
When using a partial condensation apparatus for the main production, an apparatus normally used when there is a need for using generally larger amounts of carrier steam to achieve the distillation separation from the high-boiling matter, the lower boiling components appear mainly in the radiation drain water. Although this process provides an improvement in the main production distillate quality without, however, making it possible to get total separation, the process has the disadvantages of an especially high energy demand for the condensation of the carrier steam used and a considerably larger output of drain water which is loaded with organic matter. This should be absolutely avoided, considering todays sewage output in the whole world and treatment of the drain water to eliminate the organic matter contained therein is very expensive.
According to a more recent procedure developed by the present inventor (see German Pat. No. 2352859), the separation of these components is done by means of rectification with a column which has both an effective concentration portion and a stripper portion. The stripper portion is constructed as a trickle film column in the shape of a counter current film evaporator and the concentration portion is constructed as a floor or fill column. The fill column is operated with top pressure of between 67 and 400 mbar and with a bottom temperatures in the range of 170.degree.-210.degree. C., so that the water contained in the crude acid, which evaporates at the working temperatures employed, condenses together with the only slightly water-soluble organic lower boiling components using cooling water in the temperature range of between 38.degree. and 80.degree.. The condensate is then divided into an upper lighter organic phase and a lower heavier water phase during the subsequent phase divider step and only the organic phase is fed to the head of the concentrator column in a return flow.
An object of the present invention is to achieve a more thorough and reliable separation of the precut or forerunnings (lower boiling components) as compared to the above procedure. Another object of the invention is to provide a treatment process in which the energy requirements are considerably reduced and in which the degree of pollution of the waste water is also reduced.
According to the invention, and unlike the processes in German Pat. No. 2352859, the separated precut components will not enter into the precut column, but rather forms the return flow in the concentrator part of the main distillation apparatus which is constructed as a fractionating condenser.